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198                                      FIOKA  1NDICA.
an interesting collection made by Captain Hay in the little
known district of Lahul.
The botanical provinces of the Western Himalaya may be
divided into two principal groups,, characterized both by their
climate and geographical position. Of these, the first group
consists of -seven provinces, all bounded on the south by the
plains of India, and through which the Himalayan rivers that
water them flow in a direction at right angles to the course of
the mountains. The second group of provinces consists of
five beyond the Satl^, most of which lie to the northward
of the first group, and follow a line parallel to them. These
arc the upper valleys of some of the same rivers as flow
through the first group of provinces, and owe their- existence
as" distinct regions in physical geography to the fact elsewhere
indiqatcd (page 168), that the courses of the upper parts of
the larger rivers of the Western Himalaya are parallel to the
axis of the chain.
The great elevations of the secondary chains (or spurs of
the. -main chain) that divide the upper group of provinces
from the lower, forming'the southern boundary of the upper,
prevents the access of humid winds to them, which, together
with *he greater elevation of their valleys, makes their climate
very different.
It is to be borne in mind that the necessity of thus dividing
the North-western Himalaya beyond the Sa'tlej into two pa-
rallel lines of provinces docs not indicate any great difference
between this part of tlic Himalaya an<} that to the eastward;
for, as we huvc repeatedly remarked, 'the heads of all the
larger Himalayan rivers ate^id climate. The* upper
valleys of most of these rivers, arc too small to constitute pro-
vinces, but it cannot be doubted'th'at when the physical fea-
tures of wch large rivers us the Subansiri, Aran, etc,, come to
be explored, their upper valleys .will beMbuud to constitute
provinces with a climate and vegetation intermediate in cha-
racter between those of tlte Himalaya'and Tibet.1